This invention relates to an excavator for excavating ground to form an underground continuous wall in civil engineering and construction works.
In forming such an underground continuous wall in the past, first a hole having an elliptical section having a 2 to 3 m major axis was dug in the ground to a predetermined depth by a powered bucket or a hole was dug to a predetermined depth by two or three series of auger drills. Alternatively a hole formed in a slurry was sealed with a bentonite solution to prevent further penetration of slurry, a reinforcing bar cage was set in the hole and a concrete-mix was poured into the hole to form a foundation column. Such a method was repeated to form an underground continuous wall.
With the underground continuous wall forming method of the prior art described above, the processes are complicated and hence take much time until the completion of the continuous wall. Moreover, slurry or bentonite solution layers at joints between successive columns interrupt formation of the continuous wall so that after completion of the wall, ground water tends to leak into the inside of the continuous wall through the joints. It is therefore very difficult to provide a continuous wall simultaneously having two functions as a foundation wall and a diaphragm wall.